feat(editor): recursive tree mode for the subpages node (#150)

The `subpages` node showed only one level of direct children. Add a `recursive`
attribute that renders the FULL descendant tree of the current page — fully
expanded, unlimited depth. Default `false`, so every previously-inserted node
stays flat (backward compatible). No backend changes: `POST /pages/tree` (via the
`getSpaceTree` wrapper) already returns the whole subtree as a flat `IPage[]`
(recursive CTE, permission-filtered); the nested tree is built on the client by
`parentPageId`.

- editor-ext `subpages.ts`: `recursive` attribute (parse/render `data-recursive`),
  shared by client + server so the collab ProseMirror schema keeps the attribute.
- `getSpaceTree`: arg loosened to `{ spaceId?; pageId? }` (the endpoint accepts
  either); new `useGetPageTreeQuery(pageId)` react-query hook.
- `subpages-view.tsx`: split into `FlatSubpages` (unchanged) and
  `RecursiveSubpages`; `buildSubtree` assembles the nested tree (cycle/self-parent
  guard, `sortPositionKeys` per level, root excluded) and a recursive `TreeNode`
  renders it (16px indent per depth, soft "showing N" note past 300 — data never
  capped). Shared/public context reads the already-nested shared tree, no
  `/pages/tree` request.
- toggles: bubble-menu flat⇄tree button + a second slash-menu item "Page tree".

Review follow-ups folded in: invalidate `["page-tree"]` from the create / update /
move / delete cache helpers so an open recursive tree refreshes (no stale data);
mode icon made reactive on editor transactions; `t` threaded into `TreeNode`
(no per-node useTranslation); shared-subtree hook deduped to a thin alias.

editor-ext build + client `tsc --noEmit` both clean. Backend untouched.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/editor-ext/src/lib/subpages/subpages.ts

@@ -6,7 +6,9 @@ export interface SubpagesOptions {
   view: any;
 }
 
-export interface SubpagesAttributes {}
+export interface SubpagesAttributes {
+  recursive?: boolean;
+}
 
 declare module "@tiptap/core" {
   interface Commands<ReturnType> {
@@ -31,6 +33,18 @@ export const Subpages = Node.create<SubpagesOptions>({
   draggable: true,
   isolating: true,
 
+  addAttributes() {
+    return {
+      recursive: {
+        // Existing nodes stay flat -> backward compatible.
+        default: false,
+        parseHTML: (el) => el.getAttribute("data-recursive") === "true",
+        renderHTML: (attrs) =>
+          attrs.recursive ? { "data-recursive": "true" } : {},
+      },
+    };
+  },
+
   parseHTML() {
     return [
       {